Heretofore it has been known to use metal balls to form tubular products and to form spiral indentations therein. One of these is my own U.S. Pat. No. 4,196,608 which issued on Apr. 8, 1980. While the method and apparatus described therein continue to be satisfactory, there are some applications where deeper indentations are desirable than can be produced by the teaching of U.S. Pat. No. 4,196,608 without rupturing the pipe.
One other difficulty encountered in the invention practiced in my U.S. Pat. No. 4,196,608 is that the use of a plurality of balls to perform the spiral formation of the pipe was that the spiral configurations were not always sharply defined. This is caused by differences in position of one ball with respect to another vis-a-vis the die track and also because of die wear and differential ball wear.